<!DOCTYPE html>
<style>
::-webkit-scrollbar {
  width: 20px;
  height: 30px;
  background-color: blue;
}
</style>
<script src="../../resources/run-after-layout-and-paint.js"></script>
<script>
if (window.testRunner) {
  testRunner.waitUntilDone();
  testRunner.dumpAsText();
}
runAfterLayoutAndPaint(function() {
  var content = document.getElementById('content');
  content.style.height = '1000px';
  runAfterLayoutAndPaint(function() {
    content.style.width = '1000px';
    runAfterLayoutAndPaint(function() {
      if (window.testRunner)
        testRunner.notifyDone();
    });
  });
});
</script>
Tests adding composited horizontal custom scrollbar then the vertical scrollbar.
Passes if no assertion failure.
<div style="overflow: auto; width: 500px; height: 500px; backface-visibility: hidden">
  <div id="content" style="width: 400px; height: 400px"></div>
</div>
